Skeletal Muscle ContractionSliding Filament Model

actinmyosin

Fig. 11.3

Thin (actin) filament

actin monomerG-actin(globular actin)

actin polymerF-actin(filamentous actin)

from Alberts et al.,Molecular Biology of the Cell

Fig. 11.3

Fig. 3-3 Ganong

Thick (myosin) filament

myosin molecule (“monomer”):2 heavy chains +4 light chains

Fig. 11.3

from Alberts et al.,Molecular Biology of the Cell

central bare zonecentral bare zone

Striated Muscle

A- band(anisotropic)contains thick filaments(and portions of thin filaments)

I- band(isotropic)contains thin filaments

Fig. 3-2Ganong

Fig. 3-3 Ganong

Fig. 11.1

Striated MuscleFig. 11.4

Striated Muscle

Fig. 11.2

Sliding Filament Model of Contraction

Fig. 3.3 Ganong

Fig. 11.9

Cross Bridge Cycle

Fig. 11.9

As myosin heads bind ATP, the crossbridges detach from actin, become reoriented and hydrolyze ATP to ADP and Pi.

No ATP no detachmente.g., rigor mortis

The myosin head isan ATPase.

The two most important shape-changing events are13/10 ATP binding (which

leads to detachment and reorientation)

11/12 Pi release (which leads to the power stroke)

causes Pi to be released.

Power stroke causes ADP to be released

Pi

ATP binding to myosin

Fig. 3-6 Ganong (19th edition)

The image above and the modifications to the Saladin text in the previous slideare based on Raiment et al., Science 261:50-58, 1993, and Vale and Milligan, Science 288:88-95, 2000.(see also Fig. 16.58 in Alberts et al., Molecular Biology of the Cell, 4th ed., 2002)

ATP binding is more important for reorientation than ATP hydrolysis.

Length-Tension Relationship

Increased muscle length causes decreased overlapbetween thick andthin filaments.

Increased muscle diameter causes increased separation(the lattice spacing)between thick andthin filaments.(actual mechanism still a topic of debate, see Fuchs and Martyn, Length-dependent Ca2+ activation in cardiac muscle: some remaining questions. J. Muscle Res. and Cell Motility, 26:199-212, 2005)

= normal operating length for skeletal muscle

= normal operatinglength for cardiacmuscle

Fig. 11.11

ly short